Add compiler flag example

lectures/debugging-strategies/slides.qmd

@@ -462,9 +462,49 @@ $\Rightarrow$ HPC systems usally provide native compiler plus gcc/gfortan. Try b
 
 ## Compiler flags example
 
-_Example program with issue illustrating the compiler flags_
+::::::::{.columns}
+
+:::{.column width=45%}
+
+```c
+#include <stdlib.h>
+
+int main() {
+   int number = 1;
+   int* ptr;
+   ptr = &number;
+
+   free(ptr);
+   // ERROR: Trying to free
+   // memory from stack
+
+   return 0;
+}
+```
+
+Compiling with
+
+`gcc inv_ptr.c -o inv_ptr`
+
+:::
+
+:::{.column width=55% .smaller}
+
+
+```
+inv_ptr.c: In function ‘main’:
+inv_ptr.c:8:4: warning: ‘free’ called on unallocated object ‘number’ [-Wfree-nonheap-object]
+    8 |    free(ptr);
+      |    ^~~~~~~~~
+inv_ptr.c:4:8: note: declared here
+    4 |    int number = 1;
+      |        ^~~~~~
+```
+
+:::
+
+::::::::
 
-TODO
 
 
 ## Fixing run-time errors